The present invention relates to a process for water-wetting oil-wet surfaces by applying an aqueous formulation comprising at least one wettability modifier which is a water-soluble ester of an alkoxylated saccharide to the oil-wet surface. The oil-wet surfaces may be any hydrophobic surfaces such as the rocks of subterranean oil-bearing formations.
In natural mineral oil deposits, mineral oil is present in the cavities of porous reservoir rocks which are sealed toward the surface of the earth by impervious top layers. The cavities may be very fine cavities, capillaries, pores or the like. Fine pore necks may, for example, have a diameter of only about 1 μm. As well as mineral oil, including fractions of natural gas, a deposit comprises water with a greater or less salt content.
In mineral oil production, a distinction is generally drawn between primary, secondary and tertiary production.
In primary production, the mineral oil flows, after commencement of drilling of the deposit, of its own accord through the borehole to the surface owing to the autogenous pressure of the deposit. However even in a best-case scenario, only a minor amount of mineral oil present, typically not more than approximately 10% in the deposit can be produced by primary production.
In secondary production, water may be injected into the deposit in order to maintain the pressure or to increase it again. Such a technique is known as water-flooding. It is the aim of water-flooding to force the mineral oil slowly through the cavities into the formation, proceeding from the injection borehole in the direction of the production borehole.
Techniques of tertiary oil production also known as enhanced oil recovery (EOR) include methods in which suitable chemicals are used as assistants for oil production. For instance, aqueous solutions comprising surfactants and/or thickening polymers may be injected into the formation in order to mobilize oil in the subterranean formation so that additional oil can be recovered from the formation.
One of the crucial points for a proper choice of suitable chemicals to enhance oil production is the nature of the inner surfaces of the mineral oil deposit.
In subterranean oil reservoirs having more or less hydrophilic surfaces such as sandstone reservoirs the surfaces usually are water-wet and droplets of hydrophobic oil can be caught in the pores of the formation if their diameter is greater than the diameter of the capillaries following the pore in flow direction. Said situation is indicated schematically in FIG. 1. In such a case suitable surfactants may be used to overcome the capillary forces and decrease the interfacial tension of the oil-water interface so that the oil droplet can be deformed and can be driven out of the pores by the injected aqueous surfactant solution. Surfactants suitable for this technique should cause an ultra-low interfacial tension at the oil-water interface.
In subterranean oil reservoirs having more or less hydrophobic surfaces such as for example carbonate reservoirs oil may be absorbed as very thin film on the inner surfaces of the formation, i.e. the surfaces are oil-wet. This is indicated schematically in FIG. 2. The water-permeability of such reservoirs having oil-wet surfaces typically is low due to the negative capillary pressure of water so that already the efficiency of water-flooding is low. In order to enhance oil recovery it is necessary to modify the oil-wet surface into a water-wet one by detaching oil from the oil-wet surface.
It is known in the art to use wettability modifiers for certain techniques in course of oil production.
U.S. Pat. No. 7,256,160 B2 discloses fracturing fluids for hydraulic fracturing of subterranean formations which comprise water wetting control agents. Such wetting control agents may be for instance ethylenglycol monomethyl glycol ether, alkyl sulfates, alkyl sulfonates, or alkyl glucosides.
M. Salehi, S. J. Johnson, and J. Liang, Langmuir 2008, 24, 14099-14107 discuss the use of several surfactants such as surfactin, sodium laureth sulphate, and dodecyltrimethylammonium bromide as wettability modifiers for oilfield reservoirs.
US 2010/0163234 A1 discloses a method for treating subterranean formations by injecting a fluid into the formation which comprises a particulate and an organosilane RnSiX4-n wherein R is an organic functional group, and X is halogen, alkoxy, or an acetoxygroup, and n is 1,2, or 3.
WO 2011/086360 A1 discloses treatment fluids for wetting control of multiple rock types which comprise a first surfactant having a charge, a second surfactant having an opposite charge and a compatilizer. The surfactants may be cationic surfactants such as alkyl ammonium chlorides and anionic surfactants such as alkyl ether sulfates and the compatilizer may be selected from various surfactants, including ethoxylated sorbitan fatty acid esters
A. Karimi, Z. Fakhroueian, A. Bahramian, A. P. Khiabani, J. B. Darabad, R. Azin, and S. Arya, Energy & Fuels 2012, 26, 1028-1036 disclose the use of nanofluids comprising ZrO2 nanoparticles and surface active components for wettability alteration in carbonates and for enhanced oil recovery. The formulation studied comprises surfactants based on sorbitane esters.
Several publications disclose the use of alkyl polyglucosides for oil field applications. Examples comprise WO 92/02594 A1, WO 2006/026732 A1, U.S. Pat. No. 4,985,154, or WO 2009/124922.
Y. Wu, S. Iglauer, P. Shuler, Y. Tang, and W. A. Goddard, Tenside, Surfactants Detergents 47(5) (2010), 280-280 disclose formulations of alkyl polyglucosides and sorbitan esters for improved oil recovery.
Wettabilty modfiers for oilfield applications need to fulfil a number of requirements based on the specific conditions prevailing in subterranean oil formations such as high temperatures and the existence of reservoir water having a high salt content with additional challenge arising from the presence of divalent ions such as Mg2+ or Ca2+.
WO 2010/069518 A1 discloses a process for producing polyol esters by transesterification of polyols or their alkoxylation products. The reaction is carried out in the presence of reducing mineral acids or organic acids as catalysts. In particular, the process is suitable for making products based on heat-sensitive starting materials such as saccharose. Furthermore, WO 2010/069518 A1 discloses esters of ethoxylated and/or propoxylated dextrose, saccharose, maltose and maltotriose which were made available the first time using the new process. The publication discloses several uses of the polyol esters obtained, however not the use in oilfield applications.